Synthesis of Au–Sn alloy nanoparticles for lead-free electronics with unique combination of low and high melting temperatures

Abstract

Au–Sn alloy nanoparticles (ANPs) with 16–67wt% Sn were successfully synthesized in the size range of 2–10nm using chemical reduction method. X-ray diffraction confirmed the formation of AuSn phase with hexagonal structure and was further validated by microscopy and spectroscopy techniques. Chemical reduction is a more scalable and economical technique relative to other synthesis methods for solder alloy particles; it can produce particles in nanoscale range and can be conducted at room temperature. A significant depression in the melting transition (starting from 187°C) was observed for the Au–Sn ANPs relative to the bulk eutectic point (Tm=280°C at 30% Au). Au-Sn nanoparticles offer a unique set of advantages as lead-free soldering material. In nanoparticle state, they can reflow at lower temperatures leading to less thermal stresses in adjacent electronic components during the manufacturing process. After the initial reflow and solder joint formation (bulk state), they can reclaim bulk Au-Sn properties including permanent high melting temperatures (up to 420°C) which can potentially lead to superior thermal and mechanical performance suitable for high temperature electronic applications such as military and aerospace.